1. Field of the Invention:
The present invention relates to an electrical switchgear and more particularly to an electrical switchgear with an improved control section of an operating unit.
2. Description of the Prior Art:
Gas insulated switchgears have been used for power stations, substations and switching stations in the vicinity of large cities and coastal areas. Insulating gas is sealed in a grounded tank portion of the gas insulated switchgear. FIG. 1, for example, is a side view of the gas insulated switchgear. It shows a bushing a, a main bus b, a disconnecting switch 63, an operating unit 9 and a control panel c. The operating unit 64 is disposed for operating a contact in the grounded tank, and the control panel c is used for signal transmission and reception with operating unit 9. The switches that make up such gas insulated switchgear comprise a pair of separable contacts accommodated in the grounded tank and a switch mechanism for operating these contacts and the operating unit. Since this operating unit is placed in the atmosphere, the components used in it may be affected by changes in the environment in which the gas-insulated switchgear is placed. In fact most of the troubles with existing gas-insulated switchgears originate in the vicinity of the operating unit. Specifically, in order to extract various signals for obtaining data when the gas-insulated switchgear is operated, the operating unit includes an auxiliary switch that emits the main device actuating signal, a limit switch for emitting a drive source control signal on detection of completion of the actuation of the main device, an interlock device that sets the locked condition of the manually operated switch in response to detection of the state of neighboring apparatus, a pressure switch that detects fluid pressure, which is a condition for locking the operation to safeguard the switch duty, and a density switch which detects the minimum guaranteed pressure of the insulating gas. The following problems, resulting from environmental conditions, may be anticipated in the contacts etc. that generate these electrical signals:
(1) Decrease of insulation resistance due to poor conduction or deterioration of the insulating parts resulting from corrosion of the contact parts due to corrosive gas present in the air. PA0 (2) Undesired contact of the various contacting points due to vibration during operation of the switch, and spurious signals etc. due to chattering. PA0 (3) Breakdown of the insulation caused by main circuit surges due to the switching operation of the gas-insulated switchgear switches being induced in the earthed tank and entering the control circuit part of the operating unit.
As mentioned above, an isolator switchgear requires as indispensable components a plurality of detection means comprising various electrical contacts. This is the major cause of the complexity of the operating unit. Also, in prolonged operation of the gas-insulated switchgear, damage to these contacts from atmospheric conditions such as salt, dust and corrosive gases, is unavoidable. Such damage can prevent the control circuit from operating, thus making operation impossible. A further problem is that an electrical wiring control cable is necessary to connect these electrical contacts to the control panel. This control cable is easily affected by the surge produced on switching the main circuit, because the surge, when induced into the control circuit, which operates at low voltage, may lead to destruction of components or spurious operation. Lastly, an appreciable amount of vibration is produced when the operating unit performs the switching operation, and this vibration may cause spurious operation of the various electrical contacts.